Processes for manufacturing stirred milk products typically comprise fermentation of an inoculated milk base in large stirred fermentation or culturing tanks, cooling of the final coagulum, and then storage and packaging of the final dairy product.
The cooling step after fermentation is a key step in this process. This step is necessary to stop the fermentation activity of inoculated lactic bacteria and to set the final acidity of the product. The cooling step involves a continuous agitation of the fermented mass in the tank during the transfer operation to the cooler, a pumping and a pipe transfer followed by a smoothing step using a static filter, a smoothing valve or a rotor stator machine. The cooling operation is usually performed by using a heat exchanger (e.g. plate, tube or scrapped surface heat exchangers) followed by a storage step in a tank before packing.
This step leads to a high viscosity loss due to shear stress applied during tank agitation, smoothing, pumping, pipe transfer and cooling.
The cooling temperature set point is thus determined as a compromise between the final product acidity and viscosity.
In order to increase the viscosity of the final product, some manufacturers add thickening agents to the milk base before fermentation. Nevertheless, these complements involve additional costs. Another possibility is to proceed only small amounts of dairy products. In order to control final acidity, some manufacturers also use lactose negative mutants of Lactobacillus and limited quantities of glucose on the fermentation media.
Consequently, there is a need for an alternative cost-efficient process for manufacturing fermented milk that combines high texture preservation and sustainable acidity control during storage and packing.